1. Field of the Invention
The present invention pertains to the art of metal cutting machine tools and, more particularly, to a roller cutter module adapted for use with a lathe type tool, i.e., a portable lathe, for cutting pipes or other tubular workpieces.
2. Background of the Invention
Conventional pipe and tube cutters employ tool bits that literally cut through the side wall of the workpiece material producing a chip much in the same manner as a lathe produces a chip during turning of a workpiece. Other cutters for pipes and tubular workpieces known as roller, chipless or metal displacement cutters are also known, these achieving their cutting function by forceful parting or displacement of the sidewall material of the workpiece through intense, concentrated pressure applied to a cutting line that circumscribes the workpiece. It is conventional to employ hardened circular cutters generally called cutter wheels for this purpose, with the cutter wheels attached to an appropriate mechanism for driving the wheels into the workpiece sidewall and around the periphery of the workpiece so that the workpiece material is progressively displaced and deformed until the cutter wheels progress entirely through the sidewall material of the workpiece.
The present invention is concerned with a roller type cutoff system for tubular workpieces incorporating cutter wheels that are driven about the periphery of the workpiece by a mechanism that drives the cutter wheels around the workpiece while they are forcibly fed into the workpiece material until the workpiece is entirely severed.
Prior art roller type cutters are known which can be attached to the rotating head of a lathe or other driving tool for severing pipes and tubular workpieces having generally thick sidewalls, wherein the tooling system includes means for driving the cutter wheels around the periphery of the workpiece and into the workpiece material itself in an automatic manner much in the same manner as a cutter tool bit. It is known, in such systems, that metal displacement will proceed until approximately 30-50% of the sidewall material of the workpiece has been penetrated by the cutter wheels. Provided that the workpiece is not axially restrained on both sides of the cutting plane of the cutter wheels, the force exerted by the cutting wheels against the adjacent sidewall material on either side of the cutting groove will exceed the tensile strength of the remaining uncut sidewall material beneath the cutter wheels resulting in the slight axial displacement of the workpiece located towards the free end of the plane in which the cutter wheels rotate. It is known to provide a compensating system whereby undue lateral pressure against the cutter wheels is avoided as a result of such distention of the workpiece whereby the cutting plane of the cutter wheels may shift slightly to follow the distention of the workpiece.
A particular problem exists in connection with the use of diametrically paired cutter wheels that are radially fed into the workpiece during a cutting operation wherein the workpiece is not perfectly circular in cross-section. It can be appreciated that, when such an out-of-round condition is encounted, the automatic feeding of the cutters into the workpiece results in one or the other of the cutter wheels and their associated support structures to be unduly stressed in an eccentric manner. That is, one of the cutter wheels and its associated support structure will encounter the workpiece periphery sooner than the other cutter wheel so that, if both cutter wheels are maintained at precisely the same radial distance from the centerline of the workpiece, loading of the one cutter wheel will greatly exceed loading applied to the other cutter wheel with a resultant unbalanced stress being applied to one of the cutter wheels and its associated support structure as compared with the other cutter wheel and its support structure.
It is highly desirable to provide an arrangement whereby such eccentric loading can be avoided on diametrically opposed cutter wheels and their associated support structure whereby stresses applied to both cutter wheels may be equalized even if the workpiece is slightly out-of-round.
The present invention has for its principal objective a compensating arrangement for roller cutters used for cutting workpieces that might be slightly out-of-round without imposing substantial eccentric stresses on the opposed cutter wheels.